WHITTIER — Bernice Thompson was touring the Soviet Union's Volga River last summer when the violent stomach pains hit.

The 68-year-old Thompson began vomiting blood, so alarming the ship's doctor that he sent her to the hospital in a city where the ship was docked. The diagnosis: a bleeding ulcer requiring immediate surgery.

A surgeon was summoned from another hospital 100 miles away. He performed a successful operation, removing about two-thirds of Thompson's decaying stomach. During the 18 days Thompson was hospitalized in the industrial city of Togliatti, she visited with Soviet nurses and residents, who brought her chicken soup and other gifts nearly every day.

Thompson also developed a friendship with the doctor who saved her life, Georgii Lvovich Ratner. And last week, Thompson had her chance to reciprocate when the doctor spent 10 days at her Whittier home while visiting UCLA as part of an exchange program with the Soviet Union.

"We really enjoy having him with us," said Thompson, an energetic silver-haired woman, "and of course, we're so grateful to him."

After spending several days at UCLA, where Ratner presented a paper on vascular and general surgery in the Soviet Union, the doctor toured popular Southern California attractions with Thompson and her husband, Victor. The Thompsons took him to Disneyland, the beach, Universal Studios and to Whittwood Mall in Whittier.

Ratner said he is amazed by America's technological prowess--from Michael Jackson's Captain EO movie at Disneyland to sophisticated hospital equipment. "The electronics . . . especially in operating rooms," he said in halting English.

In addition to visiting UCLA, Ratner spent time in hospitals in New York, San Francisco and Chicago as part of his month-long visit to the United States.

After hearing the Thompsons talk so much about Whittier, Ratner was especially interested in touring the city and a local hospital. Last week, Ratner spent a morning at Presbyterian Intercommunity Hospital where doctors showed him the emergency room, intensive care unit, operating rooms and other facilities. A camera on a strap dangled from one wrist, and Ratner paused several times to be photographed.

"American men . . . laugh very often and always smile," said Ratner, who despite encouragement, would only offer a slight smile for a picture.

Ratner said he is pleased to see Bernice Thompson in such good health. "This young woman had a very bad condition," he said.

Thompson said she does not remember much about her collapse, but the medical crisis last August is still fresh in the mind of her husband. "I knew it was serious," Victor Thompson said.

He spent an anxious 36 hours waiting for his wife to be transferred from the hospital's intensive care unit, where visitors are not allowed. Victor Thompson said his wife's speedy recovery resolved any doubts he had about the quality of Soviet medical care.

"Raisa herself couldn't have had care any better," Thompson said, referring to the wife of Soviet leader Mikhail Gorbachev.

Bill Surprisingly Low

Another pleasant surprise came in the form of the bill from the Soviet hospital--$3,840 for all medical expenses, which were paid by the Thompsons' insurance company. A similar hospital stay here would have cost about $32,000, according to Judy von der Neull, spokeswoman at Presbyterian Intercommunity Hospital.

The Thompsons praised the generosity shown by the residents of Togliatti, a city about 600 miles southeast of Moscow that is one of the Soviet Union's major centers for automobile production. The city provided Victor Thompson with a hotel room and an interpreter for his stay, and members of the local Friendship Society took him on short cruises of the Volga during his wife's recuperation.

Except for fewer cars on the streets, "you could take it for an American city," Victor Thompson said of Togliatti.

As the first American to be treated at Togliatti's hospital, Bernice Thompson found herself the object of some curiosity. Doctors, nurses and members of the Friendship Society paid her regular visits, and she has exchanged letters with some of them who hope to visit the United States.

"They all cried when I left the hospital," she said.

The local Togliatti newspaper even wrote a story about Bernice Thompson's surgery. The headline was, "The Price of Trust Is Life."